Cell Signaling and Cloning

How do cells differentiate? Determination 1. When a cell “chooses” a particular fate. 2. Happens via cell signaling or asymmetrical cell division. Differentiation (when the cells actually begin to change/become different from one another) 1. Caused by differential gene expression due to inductive signals 2. Results in changes in cell function, shape (morphology), location A cell first becomes “determined” via induction, later it differentiates via induction

Example of induction, determination, and differentiation at work! The pressing question… meiosis or mitosis?

Meiosis or Mitosis? How do we go from gametes to a “full-fledged” organism? Fertilization (egg + sperm meet) = zygote. Many rounds of cell division (we do need more than one cell to perform all our many functions, after all!). This cell division is called MITOSIS. Cells become specialized.

Meiosis or Mitosis? How do we go from gametes to a “full-fledged” organism? Fertilization (egg + sperm meet) = zygote. Many rounds of cell division (we do need more than one cell to perform all our many functions, after all!). This cell division is called MITOSIS. Cells become specialized.

Meiosis or Mitosis? How do we go from gametes to a “full-fledged” organism? Fertilization (egg + sperm meet) = zygote. Many rounds of cell division (we do need more than one cell to perform all our many functions, after all!). This cell division is called MITOSIS. Cells become specialized. Note: Up through the BLASTULA stage in humans, cells are UNDIFFERENTIATED Write this down!!!

How do “sex cells” become “sex cells?” A germ cell is a cell that gives rise to sex cells. The very first germ cells are called “primordial germ cells” and are initially located outside of the sex organs. (Primordial means “original” or “the first”). Primordial germ cells Migrate to sex organs. Divide while migrating. (diploid) Germ cells Meiosis Gametes (haploid)

How do “sex cells” become “sex cells?” Primordial germ cells originate near the cells in the developing embryo that eventually become the gut. Endoderm (gut) *Note: this is a cell in the “gastrula” phase

How do “sex cells” become “sex cells?” What determines which cells become primordial germ cells in the early embryo? 1. Asymmetrical cell division (in animals other than mammals and birds) 2. Induction by neighboring cells (in mammals and birds) *Note: this is a cell in the “gastrula” phase

How do “sex cells” become “sex cells?” = “sex cell molecule” 1. Asymmetric cell division

How do “sex cells” become “sex cells?” 1. Induction by neighboring cells

How do “sex cells” become “sex cells?” 1. Induction by neighboring cells Hey, you guys. Become a sex cell!

How do “sex cells” become “sex cells?” In order for a sex cell (or any cell) to become a specialized cell… 1. That cell must become determined. This happens via asymmetrical division or inductive signals from other cells. 2. Sometime later, the cell receive an inductive signal that tells it to begin to differentiate. *Note: this is a cell in the “gastrula” phase

An example of induction relating to body part differentiation

Meiosis or Mitosis? How do we go from gametes to a “full-fledged” organism? Fertilization (egg + sperm meet) = zygote. Many rounds of cell division (we do need more than one cell to perform all our many functions, after all!). This cell division is called MITOSIS. Cells become specialized. Note: Up through the BLASTULA stage in humans, cells are UNDIFFERENTIATED Write this down!!!

How do “sex cells” become “sex cells?” = “sex cell molecule” 1. Asymmetric cell division

Asymmetric Division Cytoplasmic determinants: substances in the maternal gamete (egg) that affect the course of early development by regulating gene expression, which in turn affects cell fate. Cell fate: what a cell eventually becomes. When a cell is said to be “determined,” its cell fate is decided.

Differential gene expression is NOT due to loss of genetic informaiton All of the somatic cells in an organism contain the same DNA Different types of cells express different genes. This is what makes cells different from one another. All somatic cell nuclei contain all the information needed to construct an entire organism.

How can we prove that cells do not lose genetic information as they differentiate? Cloning!

How can we prove that cells do not lose genetic information as they differentiate? Cloning Clone: An exact genetic copy of an organism. Natural clones? Identical twins!

Cloning Steps